Polarimetric investigation of materials with both linear and circular anisotropy

Abstract

We investigate light propagation through materials with both linear and circular anisotropy and find the relation of the amplitude and polarization transfer functions to the four anisotropic characteristics: linear circular birefringence, and linear and circular dichroism. We determine these four characteristics of anisotropic samples by measuring the output intensity and polarization corresponding to different input polarization azimuths and fitting the theoretical and experimental results. In our experiments we have used films of side-chain azobenzene polyesters in which optical anisotropy had been previously induced on illumination with elliptically polarized light.     

Zinc Tin Oxide (ZTO) electron transporting buffer layer in inverted organic solar cell

Solution processed, high electron mobility and highly transparent Zinc Tin Oxide (ZTO) was successfully exploited as electron transporting buffer layer in an inverted organic solar cell. The device configuration of FTO/ZTO/P3HT:PCBM/WO₃/Ag was employed. For comparison, an identical device using a sol–gel derived TiO_x electron extracting layer was also fabricated. Increased short-circuit density (J_sc) and open-circuit voltage (V_oc) were generated in the devices with ZTO layer in comparison to the ones with TiO_x layer. It is attributed to a better electron transporting, hole blocking capacities and reduced recombination probabilities at electron collecting electrode with ZTO layer. A power conversion efficiency of 3.05% was achieved with ZTO devices.     

Understanding discharges initiated by water droplet on epoxy nanocomposites under DC voltages adopting UHF technique

Corona inception voltage due to a water droplet on epoxy resin in an electrode gap is high under DC voltage compared to AC voltage. It is observed that, as the contact angle of the epoxy nanocomposite material becomes higher, the corona discharge inception voltage increases. The droplet movement is observed, using a high‐speed camera, on application of the voltage. It is seen that a droplet moves toward the ground electrode under an AC or a negative DC voltage, whereas it moves toward the high‐voltage electrode under a positive DC voltage. It is also observed that carbonization occurs near the ground electrode under AC and negative DC voltages, and near the high‐voltage electrode under a positive DC voltage. During the evaporation of the water droplet (during arcing) on the surface of the insulating material under AC and DC voltages, carbonization of material occurs and is high both in pure epoxy resin and in nanocomposites with 5 wt% epoxy clay. The magnitude of the arcing current is nearly the same irrespective of the percentage of clay in the epoxy nanocomposites. The magnitude of discharge current flow is high under negative DC voltage compared to positive DC/AC voltages. The rise time of injected current pulses, at the time of corona inception and during arcing, under AC/DC voltages, is a few nanoseconds. Ultrahigh‐frequency signals were emitted as a result of the corona discharge from the water droplet on epoxy nanocomposites and at the time of arcing between the droplets and the electrodes, both under AC and DC voltages, with its dominant frequency in the range 1–2 GHz. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Ensembles of radial basis function networks for spectroscopicdetection of cervical precancer

The mortality related to cervical cancer can be substantially reduced through early detection and treatment. However, current detection techniques, such as Pap smear and colposcopy, fail to achieve a concurrently high sensitivity and specificity. In vivo fluorescence spectroscopy is a technique which quickly, noninvasively and quantitatively probes the biochemical and morphological changes that occur in precancerous tissue. A multivariate statistical algorithm was used to extract clinically useful information from tissue spectra acquired from 361 cervical sites from 95 patients at 337-, 380-, and 460-nm excitation wavelengths. The multivariate statistical analysis was also employed to reduce the number of fluorescence excitation-emission wavelength pairs required to discriminate healthy tissue samples from precancerous tissue samples. The use of connectionist methods such as multilayered perceptrons, radial basis function (RBF) networks, and ensembles of such networks was investigated. RBF ensemble algorithms based on fluorescence spectra potentially provide automated and near real-time implementation of precancer detection in the hands of nonexperts. The results are more reliable, direct, and accurate than those achieved by either human experts or multivariate statistical algorithms     

Analytical model for time to cover cracking in RC structures due to rebar corrosion

The structural degradation of concrete structures due to reinforcement corrosion is a major worldwide problem. Reinforcement corrosion causes a volume increase due to the oxidation of metallic iron, which is mainly responsible for exerting the expansive radial pressure at the steel–concrete interface and development of hoop tensile stresses in the surrounding concrete. Cracking occurs, once the maximum hoop tensile stress exceeds the tensile strength of the concrete. The cracking begins at the steel–concrete interface and propagates outwards and eventually results in the thorough cracking of the cover concrete and this would indicate the loss of service life for the corrosion affected structures. An analytical model is proposed to predict the time required for cover cracking and the weight loss of reinforcing bar in corrosion affected reinforced concrete structures. The modelling aspects of the residual strength of cracked concrete and the stiffness contribution from the combination of reinforcement and expansive corrosion products have also been incorporated in the model. The problem is modeled as a boundary value problem and the governing equations are expressed in terms of the radial displacement. The analytical solutions are presented considering a simple two-zone model for the cover concrete, viz. cracked or uncracked. Reasonable estimation of the various parameters in the model related to the composition and properties of expansive corrosion products based on the available published experimental data has also been discussed. The performance of the proposed corrosion cracking model is then investigated through its ability to reproduce available experimental trends. Reasonably good agreement between experimental results and the analytical predictions has been obtained. It has also been found that tensile strength and initial tangent modulus of cover concrete, annual mean corrosion rate and modulus of elasticity of reinforcement plus corrosion products combined significantly influence predicted time to cover cracking. The analytical predictions of the proposed model have also been found to be in line with those of the other reported published data.     

Photoinduced circular anisotropy in side-chain azobenzene polyesters

We report for the first time the inducing of large circular anisotropy in previously unoriented films of side-chain azobenzene polyesters on illumination with circularly polarized light at a wavelength of 488 nm. The circular dichroism and optical activity are measured simultaneously in real time at two wavelengths, 488 nm and 633 nm. The photoinduced optical activity has been measured to be 10⁴ deg/cm and the circular dichroism has been found to be on the order of 0.3.     

Understanding the water droplet initiated discharges on gamma irradiated silicone rubber insulation

Corona inception voltage (CIV) due to water droplet on gamma‐irradiated silicone rubber indicates that its value reduces with increase of conductivity and with number of droplet in the electrode gap along the axis of the electrode. Increase in dosage of gamma irradiation to silicone rubber reduces the CIV. The UHF signal generated during corona inception due to water droplet has frequency bandwidth in the range of 0.3–1.2 GHz. The discharges occur in the phase range of 30°–130° in the positive half cycle and about 210°–270° in the negative half cycle. The water droplet shape gets altered on application of voltage. Surface charge accumulation studies indicate characteristic change with gamma irradiated specimen. In the presence of water droplet, the charge decay occurs rapidly with a single droplet and with three droplets. Thermal analysis of gamma radiation dosed samples reveals the destabilization of silicone material and the formation of higher order cyclic siloxane oligomers and oxygenated organics, which are expected to act as potential charge trapping sites. POLYM. ENG. SCI., 59:182–191, 2019. © 2018 Society of Plastics Engineers     

Formation of tungsten carbide nanoparticles by wire explosion process

Tungsten carbide nanoparticles (NPs) were synthesized by wire explosion process (WEP) in gas ambient as carbon source. Formation of tungsten carbide (WC_1−X) in a single step by WEP using methane and argon-acetylene mixture as carburizing medium, is detailed. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to observe the phase and morphology of the produced NPs. In WEP, morphology and phase of NPs are controlled using different levels of energy ratio, K (ratio of energy supplied to wire and sublimation energy of wire), type and pressure, P of ambience. High purity WC_1−X NPs was synthesized in methane ambience with a high K (=19) and a high P (270 kPa). A thorough study has been made to understand the impact of type of carburizing medium. Methane-acetylene mixture gave two phases of carbides. Argon-acetylene ambience provided complete carburization in specific cases. In general, the formed NPs are spherical in shape. Formation mechanism of tungsten carbide NPs is detailed in the work.     

S,N co-doped graphene quantum dots decorated TiO2 and supported with carbon for oxygen reduction reaction catalysis

Sluggish kinetics and catalyst instability in oxygen reduction reaction are the central issues in fuel cell and metal-air battery technologies. For that, highly active, stable, and low-cost non-platinum based electrocatalysts for oxygen reduction reaction are an immediate requirement in fuel cell and metal-air battery technologies. A new composite (S,N-GQD/TiO₂/C-800) is synthesized, made of sulfur (S) and nitrogen (N) co-doped graphene quantum dot (GQD) with TiO₂. This composite is supported on carbon on heating at 800 °C under N₂ atmosphere and is explored for oxygen reduction reaction (ORR) catalyst. The synthesized composite S,N-GQD/TiO₂/C-800, shows outstanding catalytic activity with an onset potential of 0.91 V and a half-wave potential of 0.82 V vs. RHE, an alkaline medium. The Tafel slope of the catalyst is 61 mV dec^?1. The catalyst is an excellent methanol tolerant and shows good stability in an alkaline medium. The excellent ORR activity of S,N-GQD/TiO₂/C-800 is ascribed to well-built interactivity between the S,N-GQD/TiO₂, and the carbon support. The unique structure offers advantages, with outstanding electrical conductivity, high surface area, and excellent charge transfer kinetics between the doped GQD and TiO₂ interface and subsequently from the carbon surface to the S,N-GQD/TiO_2.